sniffer dogs are being used to look for survivors. so far, though, the authorities have remained tight-lipped about the cause of the blast. local media are reporting that it might have been caused by an electrical fault or gas leak in an adjacent building but there's no confirmation nor denial of that. behind this police cordon, the rescue operation is continuing and preparing to carry on throughout the night. still on the scene here, there are family members of missing workers desperately waiting for news of their loved ones. and either way, this is the worst explosion in mexico city for almost 30 years. will grant, bbc news, mexico. >> now to the wise-cracking former mayor of new york who was as colorful and as exuberant as his city. ed koch was known for speaking his mind and taking on his critics. after a decade of leading the big apple in the 1980's, he's also remembered for saving the city from near financial ruin. koch died today at the age of 88 from heart failure. he was famous for asking, how am i doing? a brief time ago i a